The current practice of installing loudspeakers into vehicles such as automobiles is to fasten the loudspeakers into holes in the interior panels of the vehicular compartment.
This practice is intuitively reasonable. It uses the space between the interior panel and the outside wall (panel) of the car (between panel location). It is however, responsible for a number of well understood problems. The loudspeaker is exposed to the harsh environmental conditions that exist between the inside and outside panels of an automobile. Loudspeakers are routinely exposed to the water drainage from windows and door drains. As a result of this splash shields and waterproof loudspeaker component parts are often used. The attempts to provide environmental protection of the loudspeaker mechanism are both costly and compromise the sound quality of the loudspeaker.
With the exception of costly custom made fiberglass enclosures supplied by after market installers, the loudspeakers are allowed to operate in a near free air condition. This is a result of the very leaky air seal between the inside and outside panels in a car. Car manufacturers generally do not provide an air seal between these panels due to the requirement for water drainage openings.
Operation of the loudspeaker/woofer without acoustic loading of the rear wave radiation causes a number of problems. First, at low frequencies, only the mechanical stiffness of the suspension components control the amount of cone motion excursions. High cone excursions can damage the loudspeaker and produce poor sound quality. Second, without containment of the loudspeaker rear wave radiation, sound pressure cancellation will occur. This has the effect of greatly reducing bass and lower midrange sound output no matter what size loudspeaker is used.
The present invention is a loudspeaker assembly for controlling the rear wave radiation of a loudspeaker using an extremely compact enclosure. A cavity, preferably a spiral cavity, is formed which produces a Helmholtz acoustic element. This element provides acoustic loading and enhances bass output to frequencies well below those achieved by conventional enclosures of the same size.
The small size and shape of the loudspeaker assembly provides easy installation in a panel location without the need for a driver mounting hole. The loudspeaker assembly eliminates the problems of conventional between panel location. Loudspeaker rear wave radiation is totally contained by the enclosure so that sound pressure cancellation is eliminated.
Because part of the cavity enclosure can be formed by molding a simple depression into the interior panel, no driver mounting holes are required. Loudspeaker installation during vehicle assembly is greatly simplified.
The major benefit of this invention is a loudspeaker assembly which produces a bass sound output from a loudspeaker, in an enclosure so compact, that it can be surface mounted on the interior panel of a vehicular passenger compartment. Alternatively, it can be mounted in any flat surface, i.e. wall, ceiling, etcetera.
Broadly the invention comprises an inner sleeve to which a loudspeaker is secured. The inner sleeve is received within an outer sleeve and the inner and outer sleeves define an annulus therebetween. Channels are formed in the annulus. In the preferred embodiment (vented or bass reflex speaker) the open rear or back of the inner sleeve is spaced apart from the rear or back of the outer sleeve to form a vented volume. The air in the channels is caused, by the loudspeaker driver, to resonate with the volume of air contained within the open ended inner sleeve forming a Helmholtz element.
In an alternative embodiment a bandpass frequency response can be achieved. The loudspeaker driver is mounted in a sealed enclosure which is accomplished by closing the open rear or back of the inner sleeve. The sealed inner sleeve is spaced from the closed end of the outer sleeve in order to form an internal volume of air. The air in the channels is caused by the driver to resonate with the internal volume of air to form a Helmholtz element.
In another alternative embodiment, the inner sleeve could be modified to include its own Helmholtz element which then communicates with the internal volume of air. The air in the channels is then cause to resonate by action of the Helmholtz element of the inside sleeve with the internal volume of air producing an additional Helmholtz element.
Broadly, the channels at one end are in acoustical communication with the loudspeaker and at the other end (front end) communicate with the ambient environment (the car interior). In a particularly preferred embodiment they are spirals. However, in other embodiments they may be sinusoidal with either uniform or non-uniform waves comprising the sinusoidal wave form. If desired, the channels may be straight lined, saw toothed, crenelated, etcetera.